I have only worked with MessageBroker servlet and never RDS. I believe that you would use RTMP for streaming. I use BlazeDS and have not gotten into RTMP (yet) as I'm not doing any streaming. If I were going to be streaming, I'd use RTMP and I'd probably have lifecycle data services or a Wowza server that handles RTMP...

subject: What is the significance of message broker servlet and RDS servlet